Prosthetic or artificial valves have been developed for placement in the venous system to augment or replace native valves whose functionality has been compromised. Valves become incompetent when the cusps cannot close sufficiently to prevent reflux of blood, thereby causing it to pool in the lower extremities which often leads to painful swelling of the lower legs and feet.
Based on the initial animal and clinical experience with the placement of prosthetic venous valves to treat chronic venous insufficiency in the lower extremities, some physicians feel that placement strategies play an important role in the efficacy of the treatment. One strategy is to place the prosthetic valve near or across the native valve to take advantage of what functionality may still exist and/or derive the optimal physiological location. The deep veins of the legs typically have a elliptical cross-sectional shape due to compression by the adjacent muscles that lie on either side of the vessel. It is the action of these muscles against the vessel that help to propel the blood toward the heart. During investigational animal studies of our own early prototype venous valves, efforts were under to orient the orifice with the long axis of the vessel in the expectation that such an orientation would improve functionality of the valve. This proved difficult to accomplish under fluoroscopy since that the leaflet structure and support structure of a typical artificial valve offers little or no visual guidance to aid in aligning the orifice accordingly. While gold or other radiopaque markers have been used to identify the ends of coronary and other types of stents to aid in longitudinal positioning across a stricture, lesion, or other target site (e.g., U.S. Pat. No. 6,409,752), the need for circumferential orientation has generally not been addressed and thus, previous marker arrangements have not been designed to be particularly useful for that purpose. Needless to say, if a specific orientation of the prosthesis is critical, it must be accomplished prior to deployment, particularly if the prosthesis is self-fixating, such as by virtue of barbs or other anchoring structure.
What is needed is a prosthesis having a preferred circumferential orientation within the vessel that includes structure or some means by which the clinician can readily ascertain under fluoroscopy or some other imaging system, whether the prosthesis is correctly rotated within the vessel prior to deployment.